jump_label, x86: Introduce jump_entry_size()

This allows architectures to have variable sized jumps.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210506194157.786777050@infradead.org

arch/x86/include/asm/jump_label.h

@@ -4,8 +4,6 @@
 
 #define HAVE_JUMP_LABEL_BATCH
 
-#define JUMP_LABEL_NOP_SIZE 5
-
 #include <asm/asm.h>
 #include <asm/nops.h>
 
@@ -47,6 +45,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke
 	return true;
 }
 
+extern int arch_jump_entry_size(struct jump_entry *entry);
+
 #endif	/* __ASSEMBLY__ */
 
 #endif

arch/x86/kernel/jump_label.c

@@ -16,6 +16,13 @@
 #include <asm/alternative.h>
 #include <asm/text-patching.h>
 
+#define JUMP_LABEL_NOP_SIZE	JMP32_INSN_SIZE
+
+int arch_jump_entry_size(struct jump_entry *entry)
+{
+	return JMP32_INSN_SIZE;
+}
+
 static const void *
 __jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type)
 {

include/linux/jump_label.h

@@ -176,6 +176,15 @@ static inline void jump_entry_set_init(struct jump_entry *entry)
 	entry->key |= 2;
 }
 
+static inline int jump_entry_size(struct jump_entry *entry)
+{
+#ifdef JUMP_LABEL_NOP_SIZE
+	return JUMP_LABEL_NOP_SIZE;
+#else
+	return arch_jump_entry_size(entry);
+#endif
+}
+
 #endif
 #endif
 

kernel/jump_label.c

@@ -309,7 +309,7 @@ EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 {
 	if (jump_entry_code(entry) <= (unsigned long)end &&
-	    jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
+	    jump_entry_code(entry) + jump_entry_size(entry) > (unsigned long)start)
 		return 1;
 
 	return 0;